Only a few days ago, millions of Americans probably had never heard of psilocybin, the active agent in psychedelic mushrooms, but thanks to Denver, it is about to get its moment in the political sun. On Tuesday, the city’s voters surprised everyone by narrowly approving a ballot initiative that effectively decriminalizes psilocybin, making its possession, use or personal cultivation a low-priority crime.

The move is largely symbolic — only 11 psilocybin cases have been prosecuted in Denver in the last three years, and state and federal police may still make arrests — but it is not without significance. A measure legalizing psilocybin therapy is likely to be on the ballot in Oregon in 2020, and activists in California are mounting a second campaign to get a decriminalization measure on the ballot there. For the first time since psychedelics were broadly banned under the 1970 Controlled Substances Act, we’re about to have a national debate about the place of psilocybin in our society. Debate is always a good thing, but I worry that we’re not quite ready for this one.

No one should ever be arrested or go to jail for the possession or cultivation of any kind of mushroom — it would be disingenuous for me to say otherwise, since I have possessed, used and grown psilocybin myself. Like many others, I was inspired to do so by the recent renaissance of research into psychedelics, including psilocybin.

Scientists at places such as Johns Hopkins, New York University, Harbor-U.C.L.A. Medical Center and Imperial College in London have conducted small but rigorous studies that suggest a single psilocybin trip guided by trained professionals has the potential to relieve “existential distress” in cancer patients; break addictions to cigarettes, alcohol and cocaine; and bring relief to people struggling with depression. Psychiatry’s current drugs for treating these disorders are limited in their effectiveness, often addictive, address only symptoms and come with serious side effects, so the prospect of psychedelic medicine is raising hopes of a badly needed revolution in mental health care.

This might help explain why the Food and Drug Administration granted “breakthrough therapy” status last year to psilocybin, which promises to speed its consideration as a treatment for depression. But the research also shows that psilocybin may have value for the rest of us: Studies have demonstrated that, properly administered, a psilocybin journey can have enduring, positive effects on the well-being and relative openness of “healthy normals,” as researchers put it.

This is all very exciting, especially coming at a time when rates of depression, suicide and addiction are rising. But the history of psychedelics has been marked by periods of both irrational exuberance and equally irrational stigmatization, so a few cautionary notes are in order. As much as the supporters of legal psilocybin hope to follow the political playbook that has rapidly changed the status of cannabis in recent years, they need to bear in mind that psilocybin is a very different drug, and it is not for everyone.

In some ways, psilocybin is a remarkably safe drug — there is no known lethal dose (something that can’t be said for many medicines sold without a prescription) and it is nonaddictive. But there are risks, both practical and psychological, and these can be serious. Someone on a high dose of psilocybin is apt to have badly impaired judgment and, unsupervised, can do something reckless. Without proper attention to setting and preparation, people can have absolutely terrifying experiences, sometimes with lasting effects; a recent survey of people who reported having a “bad trip” found that nearly 8 percent of them had sought psychiatric help afterward.

There’s a reason psychedelic researchers screen volunteers carefully, excluding people at risk of serious mental illness like schizophrenia; in rare instances, a psychedelic trip can set off a psychotic break. The researchers also look at drug interactions, and often disqualify volunteers who are taking certain psychiatric medications.

I look forward to the day when psychedelic medicines like psilocybin, having proven their safety and efficacy in F.D.A.-approved trials, will take their legal place in society, not only in mental health care but in the lives of people dealing with garden-variety unhappiness or interested in spiritual exploration and personal growth.

My worry is that ballot initiatives may not be the smartest way to get there. We still have a lot to learn about the immense power and potential risk of these molecules, not to mention the consequences of unrestricted use. It would be a shame if the public is pushed to make premature decisions about psychedelics before the researchers have completed their work. There is, too, the risk of inciting the sort of political backlash that, in the late 1960s, set back research into psychedelics for decades. Think of what we might know now, and the suffering that might have been alleviated, had that research been allowed to continue.

When psychedelics like psilocybin and LSD burst upon the scene in the 1950s and 1960s, they arrived without an instruction manual. Half a century later we’re still struggling to learn how best to harness their spooky power. One source of wisdom on that question is other cultures with much longer experience using these medicines. (Just this week, archaeologists reported finding a 1,000-year-old set of tools in Bolivia bearing trace amounts of ayahuasca and other psychoactive chemicals.)

Whether in pre-Conquest South or Central America (where psilocybin has been used for centuries), or Ancient Greece, psychedelic substances were always approached with deliberateness and care. For the most part, the substances were not taken alone but usually in a group under the direction of an elder or shaman familiar with the mental territory, and they were used only on certain occasions, surrounded by ritual and with a clear intention. There was nothing casual about it.

We would do well to keep that in mind in the years ahead, as we begin the work of figuring out how to make the most constructive use of these astonishing gifts of nature.